1. Field of the Invention
The invention relates in general to decontamination systems, and more particularly to self-decontamination systems.
2. Description of the Related Art
Contamination by harmful biological or chemical agents is a common occurrence in everyday life, and decontamination is often required to render such contaminated objects safe for further handling. Conventional decontamination systems for sterilizing or cleaning objects, typically mechanical or chemical in nature, can be used to decontaminate a variety of objects such as brushes, medical instruments, military equipment, and interior or exterior walls. These systems generally include the application of a decontaminating coating to one or more surfaces on the object, or confinement of the contaminated object in a decontaminating enclosure.
One popular type of decontaminating coating contains photocatalytic material which, when exposed to UV light, generates oxidizing species that degrade biological or chemical agents. Oxidative coatings can be used in a variety of situations, including high efficiency particulate air (HEPA) filters and wall paint.
Photocatalytic oxidation is based on the production of several highly reactive, short-lived chemical species, particularly oxygen-based radicals and ions that are effective in neutralizing or destroying microorganisms and hazardous chemicals such as volatile organic compounds (VOCs). One such reaction product, ozone, has the ability to oxidize organic material, including the cell wall of a microorganism. Ozone is a reactive form of oxygen that is a strong oxidant having documented ability to kill spores, bacteria, and viruses. In addition, since ozone is released into the ambient atmosphere during oxidation, the atmosphere immediately surrounding the coating may be decontaminated at the same time as the coated surface.
Photocatalytic materials can oxidize a wide range of substances and the effectiveness of photocatalytic oxidation systems has been well documented. Photocatalytic particles, coatings, and thin films have, for example, been demonstrated to oxidize (or reduce) a very wide range of organic and inorganic compounds at ambient temperatures, pressures, and humidities. Furthermore, a targeted microorganism is usually completely destroyed during the oxidation process.
Titania exists in a number of crystalline forms, the most important of which are anatase and rutile. The photocatalytic activity of titania results in thin coatings of the material exhibiting self cleaning and disinfecting properties under exposure to UV radiation. These properties make the material a candidate for antimicrobial coatings which potentially may be used to decontaminate many different types of objects, including medical devices, food preparation surfaces, air conditioning filters, sanitary ware surfaces (e.g. toilets, sinks), articles of clothing and the like.
Self-cleaning coatings using photocatalytic titanium dioxide (TiO2) have gained considerable industry attention in recent years. TiO2 offers two unique properties: (a) strong oxidation power, and (b) super-hydrophilicity. The first property, strong oxidation power, can be used to kill bacteria attached to a wall or to oxidize/remove foul smells from stains in a toilet and, as a result, TiO2-coated tile and TiO2-coated glass are now commercially available. The second property, super-hydrophilicity, can be used to provide anti-fogging and self-cleaning properties to optical structures in that, when a TiO2 coating is applied to an exterior surface, it allows dirt and stains to be easily washed away with water or by rainfall. TiO2 microstructures also possess a high refractive index (on the order of about 1.95-1.99) and excellent transparency in the visible range. One popular approach is to apply a coating (e.g. over layer, over material) of TiO2 to catalytically decompose chemical or biological agents on the surface of an object upon irradiation with low level or long wavelength UV light sources, typically sunlight or fluorescent lamps, respectively.
Self-cleaning and/or disinfecting/sterilizing coatings, structures, and systems developed for decontamination are disclosed in U.S. Pat. Nos. 6,827,910; 6,242,862; 6,242,752; 6,135,126; 6,024,929; 6,099,813; and 5,650,126 as well as in U.S. Patent Publication Nos. 2006/0261285; 2005/0249955; 2005/0212769; 2005/0191505; 2004/0224145; 2004/0053190, and 2003/0071790. However, each one of these references suffers from one or more of the following disadvantages: the decontamination process is dependent on sunlight as the UV source (i.e. it can not be used indoors); the decontamination technique requires an enclosed space or structure such as an external housing, or an additional, permanent structural feature such as a cover plate which can alter the dimensions of the surface targeted for decontamination; the approach can be costly and/or have impractical logistical requirements such as access to UV-generating equipment and power (e.g. transporting large, fragile mercury lamps and their associated power supplies to remote locations such as battlefields); human health or safety may be compromised because the user is exposed to and/or in direct contact with UV irradiation or other harmful materials during the decontamination process; the photocatalytic products generated by the coating attack and damage the surface during the decontamination or bleaching process; the procedure requires external ingredients or materials that must be placed in physical contact with the contaminated surface in order to decontaminate it, the system has low efficiency due to its dependence on low level or long wavelength UV light sources, or the system either requires a large or rigid UV lamp as a functional component or a housing containing such a lamp.
Therefore, a need exists for systems and methods for self-decontamination which can be adapted for use, on demand if necessary, in a wide variety of applications and locations. Ideally, such systems should be safe, cheap, robust, non-destructive, portable, and flexible, as well as more efficient, smaller and/or more adaptive than current technologies.